False colour imagery

Google has recently done a minor imagery update. The only May image is a DigitalGlobe image of the Fort McMurray wildfire, although it does not include Fort McMurray itself. When we looked at the Fort McMurray wildfire a few days ago we noted that there is a wide variety of satellite imagery available. However, most of it is low resolution imagery not suitable for Google Earth and the high resolution imagery from DigitalGlobe is false colour imagery. We thought this might be a good time to make some observations about false colour imagery.

False colour imagery involves mapping different spectral bands to the colours visible to the human eye: red, green and blue. Read more about false colour imagery on Wikipedia and NASA’s Earth Observatory.

Earth observation satellites, such as Landsat and Sentinel, capture all their images in a number of bands and any image can be rendered in natural colour or various combinations of false colour. However, it would appear this is not the case for at least some of DigitalGlobe’s satellites as they often only have false colour imagery of certain events. False colour imagery is good for highlighting changes to vegetation caused by fire so DigitalGlobe had good reasons for capturing false colour imagery. But the fact that they don’t seem to have true colour imagery suggests that their satellites do not, by default, capture all wavelengths that they are capable of in every image. This is most likely due to data storage and transfer limitations on the satellites.

[ Update : We received feedback from DigitalGlobe (see the comments below) stating that they do, in fact, capture and store the visible wavelengths and if necessary could create true colour images for any location where they have false colour imagery. The reason why false colour imagery of Fort McMurray was shared is because infrared wavelengths penetrate smoke and highlight vegetation changes better than visible wavelengths (the false colour imagery we saw is most likely the Near Infrared, Red and Green bands.]

Google Earth has a surprising amount of false colour imagery. It is very common across the Sahara, Saudi Arabia and Indonesia. There are also some instances of it being used for particular events such as earthquakes and fires.


False colour greatly improves contrast in desert regions such as these sand dunes in the Sahara.


Sometimes it results in striking blues such as the above location in the Sahara that looks like the middle of the ocean.


False colour not only improves contrast but can distinguish between different types of sand, which in natural colour (the yellow areas) look nearly identical.

To find the above locations in Google Earth download this KML file.
.

About Timothy Whitehead

Timothy has been using Google Earth since 2004 when it was still called Keyhole before it was renamed Google Earth in 2005 and has been a huge fan ever since. He is a programmer working for Red Wing Aerobatx and lives in Cape Town, South Africa.






PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.

Comments

  1. What are you talking about? All DG sensors acquire all bands at the same time (not just false color)!

    • Timothy Whitehead says:

      If you know more about it we would love to hear it. I came to the conclusion that that was not the case based on the fact that DigitalGlobe has false colour imagery but not natural colour imagery of Fort McMurray after the fire.

      • Timothy

        Let me discuss our various satellites and what bands they collect:

        DigitalGlobe sensors collect imagery in regular color (Red, Green. Blue) as well as Near-Infra Red (a.k.a traditional VNIR bands) on our sensors on Geoeye1, Worldview2, Worldview3 satellites.

        Worldview2 also always collects 4 additional bands (Coastal, Yellow, Red Edge, and NIR2) on top of the 4 VNIR bands listed above.

        We can task (so not all the time) WorldView-3 satellite to collect 8 Short-wave infra-red sensors that can detect heat signatures as well.

        When you see a false color image, you can safely assume that we have definitely collected normal color image as well and much more.

        Finally, how to interpret various false color combinations (the one you typically see is NIR, Red, Green) that uses all spectral bands is a much broader discussion.

        Kumar

      • it is because NIR bands penetrate the smoke better than visible bands .. and also allow to see better the vegetation damage

  2. DigitalGlobe collects all bands at the same time, but the images on Google are 3-band subsets that get produced from the full data stack. False color is just one possible band combination.



PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.